Seats of this type are disclosed in Japanese Utility Model Laid-Open Nos. 174462/1986 and 101850/1984.
The former Japanese Utility Model Laid-Open No. 174462/1986 discloses an arrangement in which a space is provided within a lower portion of a seat back, a hip support being accommodated within the space in such a manner as to be forwardly inclinable with its lower portion serving as a fulcrum, and when an occupant assumes a seated position in which his hip region is moved forwardly, the hip support is inclined forwardly so as to project outwardly from a front surface of the seat back, thereby allowing the occupant's hip region to be supported by means of this projecting portion of the seat. With this arrangement, when the occupant feels that the support of his hip region is insufficient, it is necessary for him to rise up and seat himself again after adjustably inclining the hip support still further in the forward direction.
In the latter Japanese Utility Model Laid-Open No. 101850/1984, an arrangement is disclosed in which a space is provided within a lower portion of a seat back, a hip support being disposed within the space in such a manner as to be rotatable back and forth with an upper portion thereof serving as a fulcrum, while a seat plate is connected to a lower portion of this hip support by means of a hinge in such a manner as to be movable back and forth upon a seat cushion. With this arrangement, the occupant is seated upon the seat cushion by means of the seat plate. Accordingly, when he feels that the support of his hip region is insufficient, it is necessary for the occupant to rise up, move the hip support forward by pulling the seat plate in the forward direction, and then seat himself again.
Thus, with the above-described examples of the prior art, if the occupant rises up, he can adjust the position of the hip support in a back and forth mode; however, he cannot make an adjustment in a vertical direction. Although the hip support is designed to engage the lumbar vertebra (L-3 to L-5), the position of the lumbar vertebra (L-3 to L-5) differs depending upon the physical constitution of the occupant. The conventional apparatus therefore has the drawback in that it is impossible to obtain appropriate support for the hip region of the occupant as a function of the physical constitution of the occupant.